Method of producing magnesium ferrosilicon



United States Patent 3,375,104 METHOD OF PRODUCING MAGNESIUM FERROSILICON Melvin L. McClellan, Grand Island, N.Y., assignor to gnign Carbide Corporation, a corporation of New 7 No Drawing. Filed May 27, 1965, Ser. No. 459,456 1 Claim. (Cl. 75129) ABSTRACT OF THE DISCLOSURE Method of producing magnesium-containing ferrosilicon without excessive loss of magnesium by adding magnesium to molten ferrosilicon containing more than 53% silicon and then diluting the ferrosiliconwith iron to obtain the desired ferrosilicon composition.

The present invention relates to the production of magnesium ferrosilicon. More particularly the present invention relates to a method of adding magnesium to ferrosilicon alloys whereby substantially improved recoveries of magnesium are obtained.

A common technique for producing magnesium-containing ferrosilicon is to provide a bath of molten ferrosilicon alloy in a ladle and adding magnesium by plunging magnesium ingots into the molten metal. Other techniques are also used, but the problem of magnesium recovery is common to all in view of the relatively low boiling point of magnesium (2030 F.) with respect to molten ferroalloy (22502400 F.).

This problem of magnesium recovery is highly significant in view ofthe cost of the metal and also creates a safety hazard in that the portion of magnesium which is not dissolved in the alloy is subject to flaring.

It is therefore an object of the present invention to pro vide a process for adding magnesium to ferrosilicon alloys whereby a very high proportion of the magnesium is recovered in the alloy.

Other objects will be apparent from the following description and claims.

A process in accordance with the present invention comprises providing a molten bath of ferrosilicon containing at least 53 percent silicon; adding magnesium to the molten ferrosilicon by dissolving magnesium metal therein; and, after dissolution of magnesium, adding iron to the bath is at least 53% prior to the magnesium addition, with iron being subsequently added to adjust the final alloy composition to its desired value, magnesium recoveries can be increased to 80% and higher. The reason for this is believed to be that the higher silicon content in the starting ferrosilicon provides silicon available for the formation of Mg Si, upon the addition of magnesium, whereby the vapor pressure of magnesium is lowered and losses reduced.

The following example will illustrate the method of the present invention.

Example I Molten ferrosilicon alloy (56% Si, about 2% incidental impurities, balance iron) in the amount of 5000 pounds is provided in a ladle at a temperature of about 1400 C. At this temperature magnesium metal in the amount of 650 pounds is plunged into the ferrosilicon by attaching magnesium ingots to steel bars and holding the ingots beneath the surface of the steel bath until the magnesium ingots are dissolved, The temperature after the plunge is about 1290 C.

Steel scrap, in the form of cut up bars (1" or more in diameter and about 4" or more in length) weighing 593 pounds is added to increase the iron content, causing practically no temperature change. The alloy is then cast and analyzes about 9% Mg, 46% Si, 44% iron. The magnesium recovery is 85%.

To further illustrate the present invention, tests were conducted by making heats as shown in Table I.

Heat 1 was made in the conventional manner by plunging magnesium directly into ferrosilicon having the desired final silicon to iron ratio. Heat 2 was made by using a higher silicon ferrosilicon as the starting alloy and, after the magnesium addition, adding iron, to obtain a product of the desired composition.

In obtaining the data of Table I the heats were prepared by melting the charge in an Ajax induction furnace using a graphite crucible. For plunging the magnesium, a magnesium ingot was attached to steel bars and submerged in the melt so that the ingot was 2 or 3 inches beneath the surface and held in this position until they were dissolved.

The iron addition for heat 2 was in the form of scrap steel bars 1" in diameter by 4" long.

molten bath to increase the iron content of the mag- TABLE I nesium-containing ferroalloy to the desired value. Furnace Charge, lbs. Mg Addi- Iron Addi- The present invention is particularly directed to the Heat NO m 1011, production of magnesium-containing ferrosilicon having a 50 silicon content of about 44-50%; an iron content of about :2; fig g 3g to 45% and a magnesium content of 5 to 15%.

TABLE IA Cup Sample Final Alloy Recoveries, After Meltdown, percent Tcmp., Sample, percent percent Heat No F.

Si Fe Mg Mg Fe S1 Mg St In the past, the usual manner of preparing such an alloy, which is widely used in the manufacture of ductile As can be seen from the foregoing table, in making a magnesium-containing ferrosilicon wherein the iron and iron, was to provide a bath containing ferrosilicon silicon contents are substantially in a 1 to 1 ratio, con- (containing 44 to 50% Si) and adding magnesium metal, usually by plun ing, to provide the desired magnesium content. Magnesium recoveries following this practice were usually on the order of 65 siderably higher magnesium recovery is obtained using the practice of the present invention.

, In the practice of the present invention it is important to use heavy steel scrap, e.g., in the form of cut-up bars It has been discovered however, as part of thepresent 70 about 1" diameter by 1" long or larger, for the iron adinvention, that if the silicon content of the ferrosilicon dition so that the scrap sinks immediately to the bottom.

3 4 Light scrap, such as punchings and turnings, is not suitable (3) and, after dissolution of the magnesium, adding since this type of material tends to remain at the surface iron to the molten bath in a form that sinks beneath and leads to boiling and loss of magnesium. the surface of the iron bath to provide, upon dissolu- What is claimed is: tion of the added iron, an alloy containing substan- 1. A process for adding magnesium to ferrosilicon to 5 tially equal amounts of iron and silicon. produce an alloy containing substantially equal amounts of iron and silicon and from about 5 to about 15 percent References Cited magnesium whereby high recoveries of magnesium are 013- UNITED STATES P ATENTS tained, said process comprising:

(1) providing a molten bath of ferrosilicon containing 10 at least Percent 51.1mm DAVID L. RECK, Primary Examiner. (2) plunging magnesium metal below the surface of the molten ferrosilicon to cause magnesium to be RICHARD DEAN,Exflminerdissolved therein 3,177,071 4/1965 Ebert et a1. 75-129 

